The present invention relates to a male shaft head having spline teeth for engagement into a splined female hub or the like.
In many mechanical applications in various different technical fields, it is necessary to temporarily or releasably engage two rotatable members with each other. Predominantly this involves engaging a rotatable male shaft head into a rotatable female hub or other receiver opening. Throughout this specification, the term xe2x80x9chubxe2x80x9d will be used generally to refer to any opening or recess adapted to receive a male shaft head therein. The engagement of the male shaft head into the female hub is commonly achieved by providing one or more axially longitudinally extending keys or spline teeth on the outer circumference of the shaft head, and corresponding spline grooves or keyways on the inner circumference of the hub. The splined shaft head further has corresponding spline grooves respectively between neighboring spline teeth, and the splined hub has spline teeth respectively between neighboring spline grooves. The spline teeth of the male shaft head slidingly engage with the corresponding spline grooves in the hub, so as to connect the shaft head with the hub in a rotation- or a torque-transmitting manner.
While the above described typical splined interconnection between the shaft head and the hub provides a good positive form-locking connection for torque transmission between the two components, it is generally difficult and problematic to achieve the connection Namely, in order to insert the splined male shaft head into the splined hub, the shaft head and the hub must be precisely aligned with each other in terms of their respective radial positions and in terms of their respective rotational positions. In other words, the center axis of the shaft head must be precisely aligned with the center axis of the hub, and the splined teeth of the shaft head must be precisely rotationally aligned with the corresponding spline grooves of the hub. Otherwise, it will not be possible to insert the shaft head into the hub, due to the blocking contact of the spline teeth of the two components with each other. Moreover, if there is only a slight misalignment between the two parts, in either the rotational or radial directions, the front edges of the spline teeth will suffer wear, which becomes cumulative over the course of repeatedly connecting and disconnecting the shaft head to and from mating splined hubs.
To address some of the above problems, it is also conventionally known to provide a splined shaft head with at least one spline tooth or a spline segment including plural spline teeth, which is spring-loaded and radially deflectable relative to the remaining body of the shaft head. As such a shaft head is inserted into the hub, the spring-loaded tooth or teeth will deflect radially inwardly against the spring-biasing force in order to allow some elastic play or yielding between this tooth or teeth of the shaft head and the hub. Thereby, the spring-loaded teeth are intended to click into place in the proper alignment with the spline grooves of the splined hub due to the biasing force of the spring that urges these teeth radially outwardly. Once the spring-loaded teeth are engaged properly in the spline grooves of the hub, the remaining fixed teeth will also be properly engaged into the corresponding spline grooves of the hub to establish the full torque transmitting engagement of the shaft head to the hub.
The above described spring-loaded shaft head, however, suffers several disadvantages and problems in actual use. Particularly, the spring-loaded tooth or teeth suffer rapid wear, because the spring-loaded arrangement thereof purposely allows for misalignment and play between the spline teeth of the shaft head and the spline grooves of the hub, and then urges the spring-loaded spline teeth into the proper alignment and engagement with the spline grooves of the hub with an elastic spring-load applied thereto. Also, the moveable spring-loaded arrangement of these teeth sometimes leads to jamming of the shaft head with an improper alignment relative to the hub. As a result of the loose or yielding arrangement, and especially further in view of the resulting wear and occasional jamming, the spring-loaded shaft head cannot ensure a high degree of precision and play-free engagement between the shaft head and the hub. As a further disadvantage, such a spring-loaded shaft head suffers high costs and effort with regard to the initial manufacturing and installation thereof, and in relation to ongoing maintenance and replacement thereof, especially in view of the assembly of separate moving parts that is required.
One field of application in which it is necessary to repeatedly couple and uncouple a shaft head with one or more mating hubs is in measuring the unbalance of rotating bodies and then carrying out a balancing of the rotating bodies. A particular example is the unbalance measuring and balancing of torque converters used in the drive trains of motor vehicles and the like. Before its final installation, a torque converter must be balanced to ensure proper and smooth operation thereof. Very generally, such a torque converter comprises inner parts including a turbine, a clutch plate and a stator arranged within an outer shell. The is inner parts have typically been pre-balanced during manufacturing and assembly thereof. The outer shell, however, needs to be balanced in a final balancing step. To achieve this, a balancing machine includes a first tooling that couples to the outer shell and a second tooling that couples to the inner parts and especially the turbine. Typically, the first tooling is connected to a lower drive, while the second tooling is connected to an upper drive, which then respectively rotate the outer shell and the inner parts respectively through the first tooling and the second tooling, about a vertical rotation axis.
For measuring the unbalance of the outer shell, the outer shell and the inner parts are both rotated together, by means of the first tooling and the second tooling as mentioned above. Hereby it is critical that the inner parts must be held very xe2x80x9cstillxe2x80x9d relative to the outer shell. In other words, while the inner parts are freely rotatable relative to the outer shell, during the unbalance measuring, the inner parts must be rotated exactly in synchronism with the outer shell, so that there is no relative rotation between the inner parts and the outer shell. During this rotation, the unbalance of the torque converter unit is measured by any conventionally known method and means, generally based on the radial forces exerted by the rotating body as it rotates. Then, the inner parts are rotated or rotationally offset by 180xc2x0 relative to the outer shell and thereafter once again the outer shell and inner parts are rotated together in perfect synchronism, and the overall unbalance of the torque converter unit is measured a second time. By comparing the two unbalance measurement results, the unbalance of the outer shell itself can be derived or calculated.
Then, the unbalance data are used to control a balancing procedure, for example by removing material from or adding material to the outer shell at appropriate locations to balance out the outer shell. A further unbalance measurement procedure, or so-called audit run, is carried out after performing the balance corrective steps to ensure that the balancing steps did actually achieve a proper balancing of the outer shell.
The above application of torque converter balancing places high demands on the splined shaft head of the second tooling that engages the inner parts of the torque converter. Namely, since this balancing operation must be carried out on every torque converter, the balancing equipment tooling, and particularly the splined shaft head, is repeatedly engaged with and disengaged from the respective splined openings or hubs of successive torque converters that are to be tested and balanced in a series production manner. This leads to rapid cumulative wear of the splined shaft head as generally discussed above. Also, since the unbalance measuring operation requires extreme precision and a play-free rotational interconnection between the tooling shaft head and the torque converter turbine hub, the splined shaft head must ensure such a precise play-free engagement in the hub. Essentially the connection provided by the splined shaft in the splined hub must be absolutely stable and fixed, so that the inner parts of the torque converter substantially form a single integral unit with the shaft head and the rest of the second tooling that engages the inner parts of the torque converter. Furthermore, this precision and play-free engagement must be consistent or reproducible between the first unbalance measuring run and the audit run, or otherwise any play or the like would have an effect on the unbalance measurement and result in erroneous data giving the appearance that the balancing procedures were not effective. This would lead to a continuously repeated sequence of measuring and balancing steps without ever achieving a certifiable proper balance.
When the above described conventional splined shaft heads have been used to provide the required connection to the torque converter turbine hub in this context, they have not been able to achieve high-accuracy satisfactory results. To the contrary, the conventional splined shaft heads suffer rapid wear and a somewhat loose connection with play leading to imprecise unbalance measuring results. Also, it has been a continuing difficulty to achieve the required rotational and radial alignment of the shaft head relative to the torque converter turbine hub for engaging the shaft head into the hub. In the typical method of using such a conventional splined shaft head, the shaft head is not rotating as it is inserted axially into the hub. It must be ensured that a sufficient rotational alignment of the shaft head relative to the hub exists, before the shaft head can be axially inserted into the hub. Difficulties encountered while coupling the torque converter to the balance measuring equipment lead to extra effort and time, which in turn lead to extra costs in the overall manufacturing of the torque converters.
In view of the above, it is an object of the invention to provide a splined shaft head that improves the play-free precision and reproducibility of a form-locking engagement of the shaft head into a splined hub. The shaft head according to the invention further aims to have a simplified structure, suffer reduced wear, and avoid jamming mis-alignment, in comparison to the prior art. Another object of the invention is to provide a simplified, faster and trouble-free method of engaging a splined shaft head into a splined hub. The invention further aims to avoid or overcome the disadvantages of the prior art, and to achieve additional advantages, as apparent from the present specification.
The above objects have been achieved according to the invention in a splined shaft head having a special configuration including distinct first, second and third stages, and in a special insertion method. The first stage, which adjoins and extends rearwardly from a forward free end of the shaft head, includes an outer contour that is not rotationally symmetrical and is eccentrically offset in a first radial direction relative to a major central shaft axis of the shaft head, about which the shaft head is rotatable. This first stage allows the shaft head to be inserted into the hub without requiring perfect co-axial alignment thereof. The second stage of the shaft head adjoining the first stage includes at least one lead spline tooth that is arranged on a side of the shaft head located in the first radial direction relative to the major central shaft axis and that rotationally aligns and pre-engages the shaft head into the hub. Next, the third stage includes at least one main spline tooth that fully engages the shaft head into the hub in a torque-transmitting manner.
The insertion of the shaft head into the hub is preferably carried out by simultaneously rotating and axially advancing the shaft head relative to the hub, without requiring a precise alignment thereof. Instead, it is only necessary to coarsely align the shaft head with the hub, so that the reduced outer dimension of the first stage of the shaft head will go into the open mouth of the hub. As the forward end of the shaft head is introduced into the hub, the eccentrically offset outer contour of the first stage serves to provide a radial play between the shaft head and the hub, whereby the range of this radial play is radially eccentrically offset or un-centered in the first radial direction relative to the central longitudinal shaft axis of the shaft head. Thereby the shaft head promotes a preferential de-centering of the hub relative to the shaft axis of the shaft head in the first radial direction radially outwardly toward the lead spline teeth, i.e. so as to provide radial free play on the side of the lead spline teeth. At a minimum, the shape of the first stage, as it is inserted into the hub, prevents the hub from being de-centered in a radial direction opposite the lead spline teeth, and instead pulls the hub radially toward the lead spline teeth at least into a centered position. This ensures that the shaft head can be inserted into the hub, even if there is initially not a perfect coaxial alignment between the shaft axis of the shaft head and the rotational axis of the hub. This also ensures that the lead spline tooth or teeth of the second stage will accurately engage the splined grooves of the hub.
Namely, as the second stage is inserted into the hub, the at least one lead spline tooth will rotate and axially advance (with the rotating and axially advancing shaft head) relative to the non-rotating hub, until this at least one lead spline tooth comes into rotational alignment with a corresponding spline groove of the hub and axially advances into engagement with this spline groove to establish a pre-engagement of the shaft head with the hub, whereby the hub is then carried along to rotate with the shaft head. Preferably, the first stage overlaps with the second stage, so that the at least one lead spline tooth engages into a respective spline groove of the hub while the hub is still de-centered or provided with a de-centered radial play relative to the shaft axis of the shaft head. This de-centering and the smaller outer dimension of the first stage allows a sufficient degree of play between the shaft head and the hub during insertion of the first stage (and beginning of the second stage) into the hub, to allow the one or more lead spline teeth of the second stage to engage into corresponding spline grooves of the hub, even if the shaft head and the hub were initially not in rotational and radial, i.e. coaxial, alignment with each other. This effect is especially achieved by rotating the shaft head while axially inserting it into the hub. Thereby, the shaft head xe2x80x9cfindsxe2x80x9d its proper rotational alignment with the hub during the insertion of the first stage and then the second stage into the hub.
Once the shaft head is inserted into the hub past the first stage, the hub becomes positively centered relative to the shaft axis, in that the eccentrically offset outer contour and reduced outer dimensions of the first stage transition to a concentric cylindrical body of the shaft head. At this point, the one or more lead spline teeth have come into proper engagement in corresponding spline grooves of the hub, and thereby the shaft head and the hub are now properly aligned, both rotationally and radially, and are pre-engaged with each other. Finally, the shaft head is further inserted into the hub so that the additional full engagement spline teeth or main spline teeth come into engagement with additional spline grooves of the hub, to provide a full torque-transmitting form-locking engagement between the shaft head and the hub. At this point, the full rotational torque can be transmitted from the shaft head to the hub.
The present inventive shaft head and method for its use provide a simpler shaft head structure, and a simpler process for engaging the shaft head into a hub, in comparison to the prior art. Also, tests that have been carried out using a shaft head according to the invention have shown that the inventive shaft head suffers reduced wear, avoids jamming due to mis-alignment in a splined hub, and achieves improved precision and reproducibility of a play-free form-locking engagement of the shaft head with a hub. A surprisingly high degree of precision without play, essentially a completely rigid, as-if-integral, connection between the hub and the shaft head is reproducibly achieved.